Sound Absorption Coefficient Calculator
The total sound absorption of a room governs how reverberant it sounds. It is the sum, over every surface, of the surface area multiplied by that surface's absorption coefficient, measured in sabins. This calculator takes up to three surfaces, each with its own area and absorption coefficient, and returns the total absorption in sabins, the total surface area, and the area-weighted average absorption coefficient. These figures feed straight into the Sabine reverberation-time formula. Enter coefficients from a reliable ISO 354 data sheet for each material at the frequency of interest.
Total absorption formula
Total absorption A = sum(S_i * alpha_i)
Total area = sum(S_i)
Average coefficient = A / total area
Each surface contributes its area multiplied by its absorption coefficient. The sum is the total absorption in metric sabins. Dividing by the total area gives the area-weighted mean coefficient used in reverberation calculations.
Worked example
60 m2 at 0.1, 40 m2 at 0.8, and 20 m2 at 0.3 give A = 6 + 32 + 6 = 44 sabins over 120 m2 total area. The average coefficient is 44 / 120 = 0.37.
Absorption coefficient: frequently asked questions
What is a sound absorption coefficient?
The absorption coefficient (alpha) is the fraction of incident sound energy a material absorbs rather than reflects, between 0 (perfectly reflective) and 1 (perfectly absorptive). It is frequency dependent and measured per ISO 354 in a reverberation room. A value of 0.8 means 80 percent of the energy striking the surface is absorbed.
What is a sabin?
A sabin is the unit of sound absorption equal to the absorption of one square metre (metric sabin) of a perfectly absorptive surface. Total absorption A equals the sum over all surfaces of area times absorption coefficient: A = sum(S times alpha). It is the quantity that drives reverberation time.
How is the average absorption coefficient found?
Divide total absorption by total surface area: average alpha = A divided by total S. This single figure summarises how absorptive a room is overall and feeds directly into the Sabine reverberation-time formula together with room volume.
Why are coefficients user-editable?
Absorption coefficients depend on the material and frequency and are published in manufacturer and laboratory data measured to ISO 354. There is no single universal value, so this calculator takes the coefficient for each surface as an input you supply from a reliable data sheet.
Official sources
- International Organization for Standardization: ISO 354 sound absorption measurement.
- U.S. National Institute of Standards and Technology: nist.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.